보고 싶어(요) (the 요/yo can be removed if you are close/friendly with the person)
bo-go si-po-(yo)

The structure VERB (base form) + 고 싶다 = I want to VERB, so adding 보다 (just the 보 part cos it's the base form of the verb) to 고 싶다 literally means "I want to see you", but it is most commonly used to mean "I miss you".